Update on Texas flooding

climate change almost certainly played a role

My heart is breaking for the tragedy that’s unfolding in central Texas right now. At present, more than 70 people have died in the flooding in the Texas Hill Country.

Given the widespread interest in this event and numerous requests for comment from the media, I’ve compiled the essential points you need to know here.

The role of climate change

I’ve written about the influence of climate change in intense precipitation events before, and here’s what I said:

Let me emphasize up front that climate change doesn’t cause rain events. Rather, the role of climate change is like steroids for the weather — it injects an extra dose of intensity into existing weather patterns. So the right question is whether climate change has amped up this event.

Warmer air can hold more water vapor — about 7% more for every degree Celsius increase in temperature. Consequently, the air converging into a storm system in a warmer climate carries more water vapor. Since most of the water vapor entering the storm’s updraft will fall out as rain, everything else the same, more water in the air flowing into the storm will lead to more intense rainfall. That’s it. Not terribly complicated.

Obviously, not everything else has to stay the same. Things like the vertical velocity and the temperature profile can both change and that could modify the rate at which intense rainfall is getting more intense. See this paper for a complete discussion of these other factors. Considering all of the factors yields a very similar conclusion.

can we see this in observations? yes!

When it comes to flooding, the rain events we care about are the most intense. And this plot shows the observed frequency of occurrence of these rain events in two periods, the mid-20th century and the late-20th/early-21st century. As you can see, the heaviest events (above 99th percentile) are indeed becoming more intense.

what does the scientific community conclude?

Because of this, the IPCC’s synthesis report concluded:

The frequency and intensity of heavy precipitation events have increased since the 1950s over most land areas for which observational data are sufficient for trend analysis (high confidence), and human-caused climate change is likely the main driver.

They go on to say that:

The projected increase in frequency and intensity of heavy precipitation (high confidence) will increase rain-generated local flooding (medium confidence).

tl;dr: here’s what you need to know:

We have added a lot of carbon to the atmosphere, and that extra carbon traps energy in the climate system. Because of this extra energy, every weather event we see now carries some influence from climate change. The only question is how big that influence is.

Measuring the exact size takes careful attribution studies, but basic physics already tells us the direction: climate change very likely made this event stronger. If you disagree, the burden is on you to show me the data.

Did the National Weather Service forecast this?

Yes, they did about as good a job as you could expect. Marshall Shepherd has a write-up on on Forbes, where he said:

The National Weather Service Austin/San Antonio issued a Flash Flood Warning at 1:14 am CDT for Bandera and Kerr Counties, respectively. They made statements like, “Life threatening flash flooding of creeks and streams, urban areas, highways, streets, and underpasses.” That warning also specifically identified regions like Kerrville, Ingram, Hunt, Waltonia, Kerr Wildlife Management Area, and Lost Maples State Natural Area.

At 5:34 am Friday morning, the NWS issued a Flood Emergency for much of the region. The warning stated, “Automated rain gauges indicate a large and deadly flood wave is moving down the Guadalupe River.” The NWS communication urged people to seek higher ground.

Did the critical warnings get to people in harm’s way?

If you want to identify one place where “the system” broke down, this is it: It seems that this information did not get to those who were most going to be affected.

As Daniel Swain wrote on bluesky:

… even quite good weather forecasts do not automatically translate into life-saving predictions--there’s a lot of other work that has to take place to contextualize the forecast and ensure it gets to right people.

NYTimes link

The NYTimes wrote an article questioning whether funding cuts for the National Weather Service might have caused the forecast (which was pretty good) to not get communicated to local officials.

This is a question worth following. As Swain wrote:

… the NWS historically has done a very good job at that forecast contextualization (outreach to local governments, emergency managers, outdoor recreation facilities, etc.). But that’s one of the first things to go away when offices are critically understaffed.¹

Final thoughts

Extreme events like this are going to become more common and we must learn how to deal with them. This includes improving infrastructure to withstand more intense precipitation as well as upgrading our warning systems so people can evacuate at-risk areas safely.

Both of those cost money, which people don’t want to pay for. From the NYTimes article:

In an interview, Rob Kelly, the Kerr County judge and its most senior elected official, said the county did not have a warning system because such systems are expensive, and local residents are resistant to new spending.

“Taxpayers won’t pay for it,” Mr. Kelly said. Asked if people might reconsider in light of the catastrophe, he said, “I don’t know.”

This event also highlights a few other things. First is the value of the National Weather Service to Americans. The NWS is a treasure and everyone should appreciate the excellent meteorologists that work there. Cutting funding for it is … well, words escape me when I try to describe the stupidity.

Second, we can see why it’s essential to decarbonize and electrify our economy. Each additional ton of CO₂ we release into the atmosphere worsens many types of extreme weather.

If stabilizing the climate required enormous sacrifices or severe economic harm, caution about decarbonizing might be justified. However, that’s not the reality: We can (largely) decarbonize our economy at a surprisingly low cost.

Ultimately, the choice is clear: we can either accept a future with increasingly severe and costly weather events or we can implement solutions at modest (or zero) cost. The rational decision seems obvious.

Appendix 1: Why is the Texas Hill Country so vulnerable

There was a good write up in The Conversation about why the region that flooded, often referred to as the Texas Hill Country, is so susceptible to this kind of disaster. Among the most important reasons:

One reason Hill Country gets powerful downpours is the Balcones Escarpment.

The escarpment is a line of cliffs and steep hills created by a geologic fault. When warm air from the Gulf rushes up the escarpment, it condenses and can dump a lot of moisture. That water flows down the hills quickly, from many different directions, filling streams and rivers below.

The hills are steep, and the water moves quickly when it floods. This is a semi-arid area with soils that don’t soak up much water, so the water sheets off quickly and the shallow creeks can rise fast.

Appendix 2: Siri, show me a dumb argument

A common, misguided type of response often seen on social media looks like this:

The argument seems to be that, if a stronger rain event ever occurred in the past, then climate change cannot be enhancing this current event.

That, of course, makes literally no sense. Why in the world would an extreme event in the past mean that climate change is not making this recent event more intense?

It may have been that this recent event would have been minor without climate change, but the additional warming from humans turned it into a seriously destructive storm, albeit not a record-setting one. Or, had this Thrall event occurred in today’s warmed world, it might have been an even bigger record setter.

Ultimately, you cannot say anything about the role of climate change by pointing out that today’s rain event is not a record.

The confidence that the scientific community has that this recent rain event was affected by climate change is based on physics: We understand the physical processes that lead to more intense rain events as the climate warms.

Given this physical understanding, the default assumption has to be that climate change made this event more intense, although we do not yet know by how much. If you want to argue that climate change is not having an affect, then show me the analysis. Don’t show me that some previous event rained harder.

1. Climate deniers are pushing back on arguments that NWS budget cuts had an affect by focusing on the quality of the forecast. However, this argument misses the point — budget cuts may have hindered outreach and communication efforts after the forecast was made, preventing crucial information from reaching the people who needed it most.